Embodiments of the invention relate to airfoil profiles in gas turbines. More specifically, embodiments of the invention relate to airfoil profiles for inlet guide vanes (IGVs) of gas turbines.
In gas turbines, IGVs condition flow coming into the turbine to enhance efficiency and performance. The IGVs project from the center structure of the inlet, are arranged around the circumference of the turbine inlet, span at least part of the flow path between the inlet inner barrel or center structure and inlet casing, and work in concert with the profile of the inlet itself to deliver flow having desired characteristics to the first rotor of the turbine. For example, incoming flow direction, speed, and pressure can be directed to desired values.
In some gas turbines, the IGVs' angle of attack can be varied to control turbine flow rate. For example, the IGVs in some turbines are mounted on radial shafts that are rotated by actuators in the turbine housing to vary the IGV rotational position and angle of attack. As angle of attack increases, incoming flow rate decreases, and as angle of attack decreases, incoming flow rate increases. It has been observed that in such variable IGV arrangements, vibration of blades downstream of the IGV can vary significantly with changes in flow setting, which could reduce turbine and turbine component life. Investigation revealed that a component of the vibration is induced by non-uniform flow separation of the IGVs, and that at a reduced flow setting, IGV flow separation becomes very sensitive to inlet flow distortions. As a result, IGVs at some locations experience more flow separation than others, and the wakes of IGVs experiencing enhanced flow separation excite certain of the observed frequencies of vibration.